The present invention relates to a display device For use in an electric vehicle, which is capable of indicating a possible running range whereto the vehicle can reach with a currently remaining charge of the vehicle's battery, together with its current location on a road map displayed on a display screen.
Japanese laid-open patent publication No. 60-230013 discloses a display device that is used in a vehicle travel-guiding device for displaying a current location of the vehicle on a road map indicated on a display screen on the basis of a road map information read from storage medium by means of detecting a running distance and a running direction of the vehicle and determining a current location in a two-dimensional coordinate system. Further, that system is intended to determine a remaining quantity of fuel in a fuel tank, to determine a possible running distance therefrom on the basis of fuel consumption, to indicate a limit radius representing a possible running distance from the current location of the vehicle on the road map, to read data of previously registered fuel or gas (filling) stations existing within the area of the limit radius, and indicate them on the road map displayed on the display screen.
Japanese laid-open patent publication No. 4-368401 also discloses a battery-charge meter that detects a residual charge of a battery of an electric vehicle and indicates the measured residual charge on its display.
Problems to be solved are such that the prior art devices only measure and indicate a residual charge of a battery of an electric vehicle, but they can not clearly advise a driver how far the vehicle may further travel with the residual battery charge.
It may be considered possible to detect a residual charge in a vehicle's battery, to calculate a possible running distance of the vehicle with the residual charge on the basis of consumption rate of the battery charge for a unit running distance, to determine therefrom a possible running range from the current location of the vehicle and to display it on a road map indicated on a display screen. However, in the case of an electric vehicle it is impossible to directly determine a possible running distance of the vehicle according to a residual battery charge because the battery charge consumption necessary for climbing a slope considerably differs from one necessary for running on a horizontal roadway and, furthermore, largely depends upon all inclination angle of a slope. For example, if the vehicle has a reduced battery charge, it may have a limited current to be instantly outputted and, thereby, can not climb an upward slope that is possible for the vehicle to climb at a normal level of its battery charge.